It is known to provide moulded plastic taps for use with containers, in particular disposable containers of the type popular for supplying liquid such as water, wine or milk. One well known type of tap for this purpose is a so-called push button tap having a resilient plastic diaphragm which, when pressed, opens the valve to allow liquid to flow from the container. The resilient plastic diaphragm, commonly referred to as a xe2x80x9cpush buttonxe2x80x9d, can be arranged so that it positively urges the valve into a sealing position when manual pressure is removed therefrom. The tap is therefore self-closing.
An alternative to push button taps are the so-called xe2x80x9crotaryxe2x80x9d taps. In these, a cap is rotated to in turn rotate a stem within the tap body. Rotation of the stem causes it to uncover an aperture provided in the tap body through which or from which liquid is dispensed. The problem with rotary taps is that effective sealing of these is generally more difficult to achieve than with push button taps. Furthermore rotary taps are not self closing.
Irrespective of the type of tap used with a container, it has been found that smooth liquid flow with a stabilised flow profile can only be achieved if either the container is flexible and collapses as liquid is dispensed or the container is vented. The reason for this is that otherwise air must flow into the container to fill the space from which liquid has been vacated and equalise the pressure within the container. The inflow of air disrupts the outflow of liquid causing it to be uneven and reducing the flow rate.
It is an object of the present invention to provide a self closing tap which will give smooth liquid flow even with rigid closed containers. It is a further object to provide a tap which will maximise the flow rate and in addition give constant flow even when the container is near empty.
A tap in accordance with the invention comprises a hollow body defining a liquid and an air inlet and a liquid and an air outlet and means for dividing the interior of the body into a liquid flow passageway between the liquid inlet and the liquid outlet and an air flow passageway between the air inlet and the air outlet, the air flow passageway being at least in part separated from the liquid flow passageway, a valve system for controlling liquid and air flow in the passageways and a push button connected to the body for operating the valve system. The advantage of this is that by providing an air flow passageway which is at least in part separately formed from the liquid flow passageway, air can flow into the container simultaneously with dispensing of liquid therefrom. Thus the pressure can continuously be equalised between the interior of the container and the exterior, ambient, environment and the liquid will flow smoothly and at the maximum possible flow rate, dictated by the size of the outlet, without requiring venting of a container with which the tap is used or collapse thereof.
The air inlet and liquid outlet are generally coincident or adjacent each other. The air outlet may be adjacent the liquid inlet or it may be spaced therefrom, in particular the air outlet may be provided such that, in use with the tap fixed to a container, it is located within the container.
The valve system is preferably of the type comprising a valve seat, a valve element and a valve stem connecting the valve element to the push button.
In one embodiment the air and liquid flow passageways are both downstream of the valve seat, whilst in a second embodiment they are both upstream of the valve seat. In the first, the valve seat is provided at the liquid inlet of the tap, whilst in the second, the valve seat is provided at the liquid outlet. The second permits of an air flow passageway which extends beyond the liquid inlet and, in use, into the container with which the tap is employed. The first embodiment does not allow such an elongate air flow passageway and it was unexpected that the air flow is still sufficient to establish smooth liquid flow.
The valve stem preferably moves in guide means which may define in part the liquid flow passageway and/or the air flow passageway. The guide means assist in tap closure through guidance of the valve stem and may also defining one or both of the passageways. The guide means, in a form which is particularly suitable for the first embodiment discussed above, comprises first and second spaced guide sleeves. The advantage of this, as will be discussed further below, is that a greater portion of the valve stem is wiped during passage through the guide means and liquid thereon additionally has to traverse the air gap created by the spacing between the sleeves which reduces the chances of it entering the push button.
Very preferably in the first embodiment the tap also comprises a flexible member fixed between the valve stem and the tap body which prevents liquid access to the push button. The flexible member serves the purpose of preventing pockets of liquid being caught in the push button which can go sour and adversely affect the quality of subsequently dispensed liquid.
The tap is preferably provided with a spout which in use can be arranged vertically or generally vertically. In the first embodiment the valve stem will move generally horizontally, i.e. transversely, or generally transversely, to the spout whilst in the second embodiment the valve stem will move vertically, i.e. parallel to the axis of the spout. With the first embodiment, the spout may include a dividing wall defining the liquid outlet and the air inlet as well as, in part, the air flow passageway and the liquid flow passageway, but in the second this is not possible since it would prevent movement of the valve element within the spout to open and close the tap.
The first embodiment which may be called a front push tap in that generally manual pressure will be provided to the xe2x80x9cfrontxe2x80x9d of the container to move the valve stem horizontally, has the advantage that only a very small amount of the tap is between the container contents and the external environment. Thus the air penetration through the tap is minimised, as too is the decay of liquid carried within a container fitted with the tap. Another advantage of this embodiment is that the pressure of the liquid remaining in the container tends to close the valve element against the valve seat when manual pressure is removed from the push button.
A significant advantage of the second embodiment, which may be termed a top push version as generally manual pressure will be applied from above to move the valve stem vertically, is that no liquid will be trapped between the valve element and the liquid outlet as the valve element is at the outlet which means that there is no chance of dripping nor of any retained liquid going sour and then spoiling subsequently dispensed liquid.